The present invention relates to an active matrix type display apparatus that controls display by a sub-pixel unit by means of an active device provided for each sub-pixel, and particularly to an active matrix type organic electroluminescence display apparatus using an electroluminescence device of organic material (hereinafter described as an organic EL device) as a light emitting device (electrooptic device) for each sub-pixel.
Recently, an organic EL display apparatus using an organic EL device as a light emitting device provided for each sub-pixel has been drawing attention as a flat-panel display. The organic EL device has a structure in which an organic material is sandwiched by two electrodes, that is, an anode electrode and a cathode electrode. By applying a voltage between the electrodes, an electron is injected from the cathode electrode into the organic layer and a hole is injected from the anode electrode into the organic layer, where the electron and the hole are recombined with each other, and thereby emit light. The organic EL device can provide a brightness of several hundred to a several ten-thousand cd/m2 at a driving voltage of 10 V or lower. The organic EL display apparatus using the organic EL device as a light emitting device for each sub-pixel is considered promising as a next-generation flat-panel display.
Methods of driving the organic EL display apparatus include a simple (passive) matrix method and an active matrix method. In order to realize larger size and higher definition of the display, the simple matrix method requires that an organic EL device of each sub-pixel momentarily emit light at a high brightness, because an increase in the number of scanning lines (that is, the number of sub-pixels in a vertical direction) means a reduction in light emitting periods of each sub-pixel.
With the active matrix method, on the other hand, it is easy to realize larger size and higher definition of the display, because each sub-pixel continues emitting light for a period of one frame. A thin film transistor (TFT) is generally used as an active device for driving the organic EL device in such an active matrix type organic EL display apparatus.
A sub-pixel driving circuit (hereinafter referred to simply as a sub-pixel circuit) including the TFT and the organic EL device are formed in each sub-pixel as separate layers with one-to-one correspondence with each other. Specifically, the sub-pixel circuit including the TFT is fabricated on a substrate to form a circuit layer. A flattening film is formed on the circuit layer, and then a contact portion for electrically connecting the sub-pixel circuit with the organic EL device is created. The organic EL device formed by sandwiching an organic layer including a light emitting layer between two electrodes is further fabricated on the flattening film and the contact portion, thereby forming a device layer.
The organic layer of a low-molecular-weight organic EL device often used in the organic EL display apparatus is generally formed by vacuum deposition. When the organic EL display apparatus having the low-molecular-weight organic EL device as a sub-pixel is intended for multi-color or full-color display, the organic EL device of each sub-pixel is selectively deposited by using a metal mask or the like. Therefore, high-precision deposition techniques are required. Since deposition accuracy affects sub-pixel pitch, resolution, aperture ratio of a light emitting device, and a defect caused by misalignment in the deposition, the deposition accuracy is important in fabricating a high-brightness, high-definition, and high-reliability organic EL display apparatus.
The simplest sub-pixel arrangement of sub-pixels that emit light in colors of R (red), G (green), and B (blue), for example, in a full-color display with a pixel formed by sub-pixels having three different luminescent colors is a stripe arrangement in which light emitting portions are arranged as sub-pixel units in a stripe form, as shown in FIG. 1. Since in the stripe arrangement, every scanning line and every signal line are orthogonal to each other, the stripe arrangement has an advantage of a simple layout of wiring and the like. For deposition of the organic EL device, however, high deposition accuracy is required, since one sub-pixel in the stripe arrangement has an aspect ratio of 1:⅓ and hence has a long and narrow shape.
In the present specification, one light emitting sub-pixel is defined as a sub-pixel, and a unit of three adjacent sub-pixels of R, G, and B is defined as a pixel. Also, in a sub-pixel section formed by arranging sub-pixels in a matrix manner, a direction of arrangement of sub-pixels in each row, that is, a direction along a scanning line for selecting a row is defined as a row direction, whereas a direction of arrangement of sub-pixels in each column, that is, a direction orthogonal to the scanning line is defined as a column direction.
As another sub-pixel arrangement, there is a delta arrangement in which light emitting portions are arranged as sub-pixel units in a triangle (delta) form, as shown in FIG. 2. The delta arrangement has an advantage of providing a high apparent display resolution, and is thus often used in a display for image display. In addition, one sub-pixel in the delta arrangement has an aspect ratio of xc2xd:⅔ and hence has a near-square shape. Therefore, a margin of deposition accuracy in the delta arrangement is large as compared with the stripe arrangement.
When light emitting portions are thus arranged as sub-pixel units in the delta arrangement, the same delta arrangement is conventionally employed for sub-pixel circuits including TFTs. When the delta arrangement is employed for sub-pixel circuits, however, arranged positions of sub-pixels adjacent to each other in a vertical direction are shifted with respect to each other by half of a sub-pixel pitch. Accordingly, scanning lines and signal lines are designed so as to be bent along the sub-pixel arrangement, resulting in a complex wiring pattern. Many bends of the wiring increase susceptibility to defects, and cause a decrease in yield. In addition, in some wiring layouts, the wiring crosses a sub-pixel, which may result in a decrease in aperture ratio.
The present invention has been made in view of the above problems, and it is accordingly an object of the present invention to provide a high-brightness, high-definition, and high-reliability active matrix type display apparatus by improving reliability of sub-pixel circuits while utilizing the advantages of arranging light emitting portions as sub-pixel units in the delta arrangement.
In order to achieve the above object, according to an aspect of the present invention, there is provided an active matrix type display apparatus formed by stacking, on a substrate, a device layer formed by arranging a light emitting portion in a sub-pixel unit and a circuit layer formed by arranging a sub-pixel circuit for driving a light emitting device of the light emitting portion in the sub-pixel unit, the active matrix type display apparatus including: a stripe sub-pixel arrangement (hereinafter referred to as a stripe arrangement) in which the sub-pixel circuits exist on straight lines in both a row direction and a column direction; and a delta sub-pixel arrangement (hereinafter referred to as a delta arrangement) in which the light emitting portions have twice a sub-pixel pitch in the row direction of the sub-pixel arrangement of the sub-pixel circuits and xc2xd of a sub-pixel pitch in the column direction of the sub-pixel arrangement of the sub-pixel circuits, and a phase difference in sub-pixel arrangement between two rows adjacent to each other is xc2xd of a pitch in the row direction of the light emitting portions.
The delta arrangement in the active matrix type display apparatus has advantages of providing a high apparent display resolution, enabling high-precision deposition of the light emitting devices, and thus being able to improve reliability of the light emitting devices. Therefore, the delta arrangement as the sub-pixel arrangement of the light emitting portions can contribute to realizing higher definition and higher brightness of the display. On the other hand, the stripe arrangement as the sub-pixel arrangement of the sub-pixel circuits reduces bends of the wiring, which results in a simpler wiring pattern, and can thus enhance reliability of the sub-pixel circuits.